One method of handling a large volume of foods, such as, for example, fruits and vegetables, is after selection, to transport these various food stuffs by an aqueous medium to transport the food stuffs through various cleaning, handling, and processing steps and environments. For example, in specific applications, fresh fruits and vegetables can be transported through water streams by food handling equipment used at a processing plant. After picking, fruits and vegetables are introduced into a flume system wherein water acts as a transport medium and a cleaning medium. Water can be used to support and transport the fruits or vegetables from an unloading site to a final storage or packing or processing location. During the transport, water can take a food item from an initial location through a series of somewhat separate stages to a final station where the produce is removed from the water and packed. The water within each stage may carry a varying degree of organic load in the form of any number of sediments and soluble materials. This water is generally recycled.
Water can also be used in some of processing stages to further clean, cool, heat, cook, or otherwise modify the food in some fashion prior to packaging. Process water as defined above can sometimes be used once and discarded. However, often times a major portion of this process water is re-used and is, therefore, subject to organic and microbial contamination. In some stages this process water stream is also used to transport the food. In other stages, the process water can be a separate stream and is recycled apart from the transport water. In either situation, the process water becomes contaminated with organic matter from the food, providing nutrients for microbial growth in the water.
Given the nature of the food as well as the presence of sediments and soluble materials, the water, flume, and other transport or processing equipment may be subject to the growth of unwanted microorganisms. Water that is untreated and recycled during transport or processing accumulates debris and increased microbial populations. Left untreated, recycled water tends to clean produce early in a shift but contaminates produce later in the shift. In fact, flume water has been identified as a potential source of coliform, E. coli and Salmonella contamination or cross contamination during cider production. These and other microorganisms are generally undesirable to the food, the water, the flume and can cause buildup on all water contact surfaces of slime or biofilm, which requires frequent cleaning to remove.
Microbial contamination or cross contamination of fruits and vegetables via water continues to be a major concern for produce packers, processors and end users. Although washing fresh produce with water can reduce potential contamination, the wash water can also serve as a source of contamination or cross contamination. If pathogenic microorganisms in water are not removed, inactivated or otherwise controlled, they can spread to surrounding produce, potentially contaminating them. Further, handling or processing steps that pool many individual fruits or vegetables tend to increase the risk that a single contaminated item may contaminate the entire lot. Immersing or spray-washing fruits and vegetables in fresh water can help reduce surface populations of microorganisms. However sterilization by repeated washing, even with sterile water, cannot be achieved because microorganisms within tissues of produce remain in place.
The addition of antimicrobial agents to recycled handling or process water can inactivate most vegetative cells in water, helping avoid cross contamination. Ideally, an antimicrobial agent or compound used in such a system will have several important properties in addition to its antimicrobial efficacy. The compound or agent should have no residual antimicrobial activity on the food. Residual activity implies the presence of a film of antimicrobial material which will continue to have antimicrobial effect which may require further rinsing of the food product. The antimicrobial agent preferably should also be odor free to prevent transfer of undesirable odors onto food stuffs. If direct food contact occurs, the antimicrobial agent should also be composed of food additive materials which will not effect food if contamination occurs, nor affect humans should incidental ingestion result. In addition, the antimicrobial agent should preferably be composed of naturally occurring or innocuous ingredients, which are chemically compatible with the environment and cause no concerns for toxic residues within the water.
In the past, transport and process water apparatus have generally been treated with sodium hypochlorite and chlorine dioxide. Generally, these materials are effective in preventing the unwanted growth of microorganisms. However, the use rate of these chlorine-based antimicrobials is very high because they tend to be rapidly consumed by the high organic load included in both the fruits or vegetables and soil. Further, upon consumption, compounds such as chlorine dioxide decompose producing byproducts such as chlorites and chlorates, while hypochlorite produces trichloromethanes which may be toxic in very low concentrations. Lastly, chlorine dioxide is a toxic gas with an acceptable air concentration limit of 0.1 ppm. Exposure to ClO2 often leads to headaches, nausea, and respiratory problems, requiring expensive and intricate safety devices and equipment when it is used.
Further, the efficacy of these common antimicrobial agents on the surface of fruits and vegetables is often limited. For example, some workers have reported that chlorine dioxide effectively controlled microbial build-up in the cucumber hydrocooling water but had little effect on microorganisms on or in the fruit. Other workers showed that chlorine treatment had little effect on surface microflora of tomatoes and oranges during a packing operation. Another group concluded that commonly used antimicrobial agents have only minor effects and should not be relied upon to eliminate microorganisms from produce. Washing raw produce with chlorinated water is effective in reducing the microbial load, as long as the proper amount of residual chlorine is maintained.
An antimicrobial agent being used more commonly in fresh produce transport or process water is peroxyacetic acid. The EPA approved a peroxyacetic acid-based composition in 1996 for controlling microbial growth and reducing biofilm formation in fruit and vegetable transport or process waters. From a historical perspective, peroxyacetic acid has been used for food contact surface sanitizing, aseptic packaging and medical device cold-sterilization, among other things. In addition to its biocidal properties, the environmentally-friendly decomposition byproducts and good stability in the presence of vegetable debris helped gain acceptance of this technology among fruit and vegetable packers, handlers, and processors.
Nevertheless, there remains a need for improved antimicrobial compositions for treating waters used for transporting or processing fruits or vegetables.